Shielding device for signal transmission coil

ABSTRACT

Systems and apparatuses are used to transmit data between external and internal portions of auditory prostheses or other medical devices. The external portion of the auditory prosthesis includes a magnet and an implanted coil that provides stimulation to the device recipient. A shaped shield material can be placed between the external coil and the sound processing hardware to improve efficiency and effectiveness between the external coil and implanted coil. Adverse effects on tuning frequencies can be reduced by disposing the shield material away from the magnet.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/807,473, filed Jul. 23, 2015, now U.S. Pat. No. 10,843,000, entitled,“SHIELDING DEVICE FOR SIGNAL TRANSMISSION COIL”, which claims thebenefit of U.S. Provisional Patent Application No. 62/028,133, filedJul. 23, 2014, entitled, “SHIELDING DEVICE FOR SIGNAL TRANSMISSIONCOIL.” The disclosure of these priority applications are herebyincorporated by reference in their entirety into the presentapplication.

BACKGROUND

Auditory prostheses, such as cochlear implants, include an implantableportion having a stimulating assembly with an implanted coil and anexternal portion having a coil, speech processing hardware and software,as well as a battery. Magnets are also disposed in both portions to holdthe external portion proximate the implanted portion. A shield offerrite or other magnetic material is installed between the externalcoil and the speech processing hardware to improve radio frequency (RF)link efficiency and effectiveness with the implanted coil. This shield,however, can make the coil-tuned frequency unacceptably sensitive to themagnetic flux from the external magnet.

SUMMARY

Embodiments disclosed herein relate to systems and apparatuses that areused to transmit data between external and internal portions of medicaldevices. Those devices include, for example, cochlear implants or otherauditory prostheses or devices. The external portion of the auditoryprosthesis includes a magnet and is powered by an on-board battery andsends signals via a coil. An implanted coil receives the signals andprovides stimulation to the device recipient. A shaped shield materialcan be placed between the external coil and the sound processinghardware to improve efficiency and effectiveness with the implantedcoil, and minimize adverse effects caused by the magnet.

This summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

BRIEF DESCRIPTION OF THE DRAWINGS

The same number represents the same element or same type of element inall drawings.

FIG. 1 is a perspective view of an auditory prosthesis, including animplantable portion and an external portion.

FIG. 2 is a perspective view of an external portion of an auditoryprosthesis.

FIG. 3 is an exploded perspective view of an external portion of anauditory prosthesis.

FIG. 4 is a side sectional view of the external portion of FIG. 3.

FIG. 5A depicts a test model of an external portion of an auditoryprosthesis.

FIG. 5B depicts results from a test of frequency ranges based on aninner shield diameter, in an auditory prosthesis.

FIGS. 6A-6B depict top section views of alternative coil shapes forcoils utilized in external portions of auditory prostheses.

DETAILED DESCRIPTION

While the technologies disclosed herein have particular application inthe cochlear implant devices depicted in FIG. 1, it will be appreciatedthat the systems, methods, and apparatuses disclosed can be employed inother types of hearing prostheses. For example, the technologiesdisclosed can be utilized in devices such as active transcutaneous boneconduction devices, passive transcutaneous devices, middle ear implants,or other devices that include an external coil and an internal orimplanted coil. Furthermore, the embodiments disclosed herein can beutilized to transmit signals to medical devices other than hearingprostheses. The technologies disclosed herein will be describedgenerally in the context of external portions of medical devices wherethe external portions utilize a coil for transmission of data and/orother signals. Such signals can also include signals sent by a chargingcoil that charges a totally-implantable cochlear implant or othermedical device. For clarity, however, the aspects disclosed herein willbe described in the context of cochlear implant auditory prostheses and,more specifically, the external portions and coils used therewith.

FIG. 1 is a perspective view of an auditory prosthesis 100, in thiscase, a cochlear implant, including an implantable portion 102 and anexternal portion 104. The implantable portion 102 of the cochlearimplant includes a stimulating assembly 106 implanted in a body(specifically, proximate and within the cochlea) to deliver electricalstimulation signals to the auditory nerve cells, thereby bypassingabsent or defective hair cells. The electrodes 110 of the stimulatingassembly 106 differentially activate auditory neurons that normallyencode differential pitches of sound. This stimulating assembly 106enables the brain to perceive a hearing sensation resembling the naturalhearing sensation normally delivered to the auditory nerve.

The external portion 104 includes a speech processor that detectsexternal sound and converts the detected sound into a coded signal 112through a suitable speech processing strategy. The coded signal 112 issent to the implanted stimulating assembly 106 via a transcutaneouslink. The signal 112 is sent from an external coil 114 located on theexternal portion 104 to an implantable coil 116 on the implantableportion 102, via a radio frequency (RF) link. The signal 112 can bedata, power, audio, or other types of signals, or combinations thereof.Coils 114, 116 can be circular, substantially circular, oval,substantially oval, D-shaped or have other shapes or configurations. Theefficiency of power transfer and integrity of the data transmission fromone coil to the other is affected by the coil coupling coefficient (k).Coil coupling coefficient k is a unitless value that indicates theamount of the shared magnetic flux between a first coil and a second,coupled (associated) coil. As the amount of shared magnetic fluxdecreases (i.e., as the coil coupling coefficient k decreases),efficient power transfer between the two coils becomes increasinglydifficult. Therefore it is advantageous to maximize the coil couplingcoefficient k in a system where power and/or data are transferredbetween two coils. The stimulating assembly 106 processes the codedsignal 112 to generate a series of stimulation sequences which are thenapplied directly to the auditory nerve via the electrodes 110 positionedwithin the cochlea. The external portion 104 also includes a battery anda status indicator 118. Permanent magnets 120, 122 are located on theimplantable portion 102 and the external portion 104, respectively. Inthe depicted device, the external portion 104 includes a microphone portconnected to a microphone that receives sound. The microphone isconnected to one or more internal processors that process and convertthe sound into stimulation signals that are sent to the implantableportion 102.

FIG. 2 is a perspective view of an external portion 200 of an auditoryprosthesis. The external portion 200 includes a body 202. For context,approximate locations of various elements disposed in the body 202 aredepicted, although those elements would not necessary be visible fromthe outside of the body 202. More detailed figures depicting the variouselements are depicted below. An external coil 204 is disposed in thebody 202, as is a permanent magnet 206, as described above. The externalportion 200 can include an indicator 208 such as a light emitting diode(LED). A battery door 210 covers a receptacle that includes a batterythat provides internal power to the various components of the externalportion 200 and the implantable portion.

It is desirable that auditory prostheses maintain a high coil qualityfactor (Q). Coil quality factor Q is a unitless value that indicates thehow much energy is lost relative to the energy stored in the resonantcircuit that includes the coil. A higher coil quality factor Q indicatesa lower rate of energy loss relative to the stored energy of theresonant circuit. Coil quality factor Q can be calculated for an idealseries RLC circuit as depicted in Equation I:

$Q = {{\frac{1}{R}\sqrt{\frac{L}{C}}} = \frac{\omega_{0}L}{R}}$Here, L is the measured inductance of the coil, R is the measuredresistance of the coil, and ω₀=2×Pi×Frequency. As the coil qualityfactor Q decreases, it becomes increasingly difficult to transfer powerefficiently from one coil to an associated coil. Therefore, it isadvantageous to maximize the coil quality factor Q in a system wherepower is transferred between two coils.

A high coil quality factor Q is desirable, even while the electronicsand batteries are in close proximity to the coil, as depicted in FIG. 2.Placing metallic components, e.g., a battery, above the coil 204, asdepicted in FIG. 2, can have an adverse effect on coil Q. A reduced coilQ, however, results in a lower efficiency RF link, which ultimatelyresults in a shorter battery life. To address this in the configurationdepicted in FIG. 2, a shield material such as a ferrite, ferrimagnetic,or ferromagnetic material can be disposed above the coil 204. Any othermaterial that substantially redirects the magnetic flux generated by thecoil 204 can also be utilized. Materials that redirect magnetic fluxcan, in certain embodiments, be defined by a high magnetic fluxpermeability. This can help alleviate the adverse effect on coil Q, butadds weight and size to the device, which is also undesirable, since theexternal portion 200 is worn on the head of a recipient. It alsoadversely affects the tuning frequency of the coil. Configuration andplacement of the shield material to address issues related to weight,tuning frequency, etc., is described in more detail below. In additionto external coil quality factor Q, the relationship between the tunedfrequency of the external coil and implantable coil has a significantimpact on the efficiency and effectiveness of the RF link. The tunedfrequency of the external coil and implantable coil are selected tobalance the needs of RF data integrity and power transfer. Anysignificant deviation from these selected tuned frequencies can reducethe efficiency and effectiveness of the RF link.

FIG. 3 is an exploded perspective view of an external portion 300 of anauditory prosthesis, while FIG. 4 depicts a side sectional view of theexternal portion 300. These two figures are described simultaneously.The external portion 300 includes a body 302 that includes an upper wall304 and an outer wall 306. A base 308 defines the lower extent of theexternal portion 300 and together with the body 302 defines a body orhousing volume V, in which the various components are contained. Inembodiments, the housing volume V can be further parsed into twodiscrete volumes, an outer volume V_(O) and an inner volume V_(I). Theouter volume V_(O), in the depicted embodiment, contains an externalcoil 310 and a shield 312 disposed above (relative to the base 308) theexternal coil 310. Each of the external coil 310 and a shield 312 areannular in shape. The outer volume V_(O) is defined by an inner coiledge 310 a. In other embodiments, the outer volume V_(O) is defined byan inner shield edge 312 a. In certain embodiments, the outer volumeV_(O) can be defined by an outer coil edge 310 b or an outer shield edge312 b. In other embodiments, the outer volume V_(O) can be at leastpartially defined by the outer wall 306. A substrate 314 that supportsthe various speech processing components 316 and the base 308 furtherdefine the upper limits of the outer volume V_(O). Thus, the spacedefined by the substrate 314, the base 308, the inner coil edge 310 a,and either of the outer coil edge 310 b and the outer wall 306 definesthe outer volume V_(O) and contains the coil 310 and shield 312. Theinner coil edge 310 a and the inner shield edge 312 a, along with thesubstrate 314 and the base 308, also define the inner volume V_(I). Theinner volume V_(I) contains a magnet 318 that, in certain embodiments,is cylindrical in shape and has an outer magnet edge 318 b.

In certain embodiments, the coil 310 and shield 312 are arranged andsized so as to be aligned. For example, the inner coil edge 310 a can bealigned with the inner shield edge 312 a. Similarly, the outer coil edge310 b can be aligned with the outer shield edge 312 b. The outer magnetedge 318 b is smaller than the inner coil edge 310 a, so that the magnet318 is completely disposed within the space defined by the inner coiledge 310 a. Center points of each of the coil 310, the shield 312, andthe magnet 318 can be aligned along an axis A that is substantiallyorthogonal to both the base 308 and the substrate 314. The crosssectional shapes (e.g., parallel to the base 308) of each of the outervolume V_(O) and the inner volume V_(I) can be defined by the shape ofthe coil 310 and shield 312. The depicted coil 310 and shield 312 arecircular in shape to maximize the coupling of magnetic flux produced bythe external coil 310 and the associated implanted coil (not shown).Other coil 310 and/or shield 312 shapes, such as substantially circular,oval, substantially oval, and D-shaped, can be used. The depictedcircular shape at least partially defines an outer volume V_(O) having asubstantially annular cross section, along with an inner volume V_(I)having a substantially cylindrical cross section.

The outer volume V_(O) and inner volume V_(I) are characterized bydifferences in magnetic permeability. Each of the coil 310 and themagnet 318 generate a magnetic flux. The magnetic permeability of theouter volume V_(O) is based at least in part on the presence of theshield 312, which substantially redirects the magnetic flux generated bythe coil 310 and therefore, has a higher magnetic permeability than theinner volume V_(I). The magnetic permeability of the inner volume V_(I)is based at least in part on the absence of any material thatsubstantially redirects the magnetic flux generated by the magnet 318.In certain embodiments, the magnet 318 is separated from the innershield edge 312 a by a gap of gas. This gas can be air, which has amagnetic permeability less that the material utilized in the shield 312.Thus, the inner volume V_(I) contains only the magnet 318. In otherembodiments, the magnet 318 is separated from the inner coil edge 310 aby a gap of air, but a portion of the shield 312 can be disposed in theinner volume V_(I), such that the inner volume V_(I) contains only themagnet 318 and a portion of the shield 312. In other embodiments, theinner volume V_(I) contains a foam or other flexible or semi-flexiblematerial that defines spaces for receiving the gas. The foam can serveas an insulating or cushioning material. In general, the magnetic fluxpermeability of any material dispersed in the inner volume V_(I) will beless than that of the shield material, but slightly greater than thegas. Regardless, one characteristic of the present aspects disclosedherein is the absence of any material proximate the magnet (e.g., abovethe magnet 318) to alter or redirect the magnetic flux thereof.

Many prior art medical devices, such as cochlear implants and otherauditory prostheses, utilize a shield material between an electronicsmodule and one or more internal components that generate magnetic flux,for example, magnets, coils, etc. Magnetic flux can interfere with theoperation of the electronics module. Additionally, having magnetic fluxpassing through the electronics module can limit effectiveness orefficiency of RF links between mating or matching coils (e.g., betweenexternal coils and implanted coils). If the inner diameter of thisshield material is small, the tuned frequency of the external coil canbe unacceptably sensitive to changes in magnet strength. Recipients of acochlear implant system have the option to select a magnet having adesired strength to provide sufficient retention and comfort. Theability to change weaker magnets for stronger magnets can be desirabledue to the variability of recipient skin flap thickness after surgery.That is, thicker skin flaps can necessitate stronger magnets. With thissmall inner diameter shield, tuning ranges of 300 kHz are observed fromthe weakest to the strongest magnet strength. This deviation from thenominal selected tuned frequency means that recipients with stronger andweaker magnets will suffer from a less efficient and less effective RFlink.

Increasing the inner diameter of the shield material in this manner canbe effective in reducing the change in tuned frequency due to the changein magnet configuration. This can result in a 60 kHz tuning range fromthe weakest magnet configuration to the strongest, which meansrecipients with stronger and weaker magnets can experience a moreeffective and efficient RF link. This maximizes retention magnet optionsfor recipients while preserving intended RF link performance. Theaspects disclosed herein also reduce need for retention magnetrepositioning, with attendant thickness increase implications.

Testing has confirmed that an absence of shielding material in the innervolume V_(I) of an external portion of a cochlear implant configured asdescribed herein significantly decreases the change in tuned frequencyexperienced by the external coil. FIG. 5A depicts a test model of anexternal portion 500 of a cochlear implant, shown in section. Here, theexternal portion 500 test model includes an external coil 502 with ashield 504 disposed above the coil 502. A magnet 506 is disposed withinan inner volume V_(I) defined by a shield inner diameter ØS of theshield 504. In general, the shield inner diameter ØS is smaller than thecoil inner diameter Ø_(C). FIG. 5B depicts the effect on frequency rangefor a shield having various shield inner diameters Ø_(S). No magneticshielding material (such as above or around the magnet 506) wasotherwise disposed in the inner volume V_(I). Interestingly, coil tunedfrequency range decreases as the shield inner diameter Ø_(S) increases.Thus, an external portion of an auditory prosthesis having a shieldinner diameter Ø_(S) substantially equal to a coil inner diameter Ø_(C)would likely have the lowest tuned frequency range.

These results are particularly compelling for coils used in the externalportions of auditory prostheses that are configured to utilize aplurality of replaceable magnets having varying strengths. For example,as described above, in a cochlear implant auditory prosthesis, anexternal portion is located and retained on the head, proximate animplanted portion. Typically, this retention is due to the utilizationof magnets, one in the external portion, and one in the implantedportion. The thickness of a skin flap between the external portion andthe implanted portion can vary significantly depending on implant depth,skin thickness, or other factors. This often requires the use of magnetshaving different strengths, with magnets having the strongest strengthsbeing used, for example, due to thicker skin flaps. Thus, a singleexternal processor can be used with a number of magnets having differentretention strengths. With reference to FIG. 5A, changing the strength ofthe retention magnet 506 in the external portion 500 changes the amountof retention magnetic flux that permeates the shield material 504disposed above the coil 502, which in turn changes the inductance of thecoil 502 and thereby changes its tuned frequency. The tuned frequencyhas a significant impact on the effectiveness and efficiency of the coil502.

The results in the graph depicted in FIG. 5B indicate that increasingthe inner diameter Ø_(S) of the shield 504, such that shielding materialis disposed further away from the magnet 506, significantly decreasesthe change in tuned frequency experienced by the coil 502 with changingretention magnet strength. In an embodiment, increasing the shield innerdiameter Ø_(S) so as to be substantially equal to the coil innerdiameter Ø_(C), distances the shield 504 as far from the magnet 506 aspossible, while still providing the shield 504 between the coil 502 andthe electronics disposed in the external portion 500, above the coil502. This decreases the impact of changing retention magnet strength oncoil effectiveness and efficiency.

FIGS. 6A-6B depict top section views of alternative coil shapes forcoils utilized in external portions of auditory prostheses. Two externalportions 600 a, 600 b are depicted. In FIG. 6A, the external portion 600a includes an outer housing 602 a and a magnet 604 a disposed therein. Acoil 606 a having an oval shape is also depicted. Thus, the inner volumeV_(I) is defined at least in part by an inner edge of the coil 606 a andthus has a generally cylindrical volume having an oval cross-sectionalshape. As described herein, an outer volume V_(O) is defined by theinner edge of the coil 606 a and either an outer edge of the coil 606 aor the housing 602 a. In FIG. 6B, the external portion 600 b includes anouter housing 602 b and a magnet 604 b disposed therein. A coil 606 bhaving a substantially D-shape is also depicted. Thus, the inner volumeV_(I) is defined at least in part by an inner edge of the coil 606 b andthus has a generally cylindrical volume having a D-shapedcross-sectional. As described herein, an outer volume V_(O) is definedby the inner edge of the coil 606 a and either an outer edge of the coil606 b or the housing 602 b. In other aspects, inner and/or outer edgesof coils and shields can be substantially round or substantially oval.

This disclosure described some embodiments of the aspects disclosedherein with reference to the accompanying drawings, in which only someof the possible embodiments were shown. Other aspects can, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments wereprovided so that this disclosure was thorough and complete and fullyconveyed the scope of the possible embodiments to those skilled in theart.

Although specific aspects were described herein, the scope of thedisclosed embodiments are not limited to those specific embodiments. Oneskilled in the art will recognize other embodiments or improvements thatare within the scope of the present technology. Therefore, the specificstructure, acts, or media are disclosed only as illustrativeembodiments. The scope of the technology is defined by the followingclaims and any equivalents therein.

What is claimed is:
 1. An apparatus comprising: a coil comprising aninner coil diameter; a substantially annular shield comprising an innershield diameter, wherein the substantially annular shield comprises afirst magnetic flux permeability, and wherein the inner coil diameterand the inner shield diameter at least partially define a volume; amagnet at least partially disposed within the volume; and a gas disposedwithin the volume, wherein the gas comprises a second magnetic fluxpermeability less than the first magnetic flux permeability.
 2. Theapparatus of claim 1, wherein the gas comprises air.
 3. The apparatus ofclaim 1, wherein the gas is contained within a material comprising athird magnetic flux permeability less than the first magnetic fluxpermeability.
 4. The apparatus of claim 1, wherein the magnet comprisesa magnet center point, wherein the magnet center point is substantiallyaligned with a coil center point of the coil and a shield center pointof the substantially annular shield.
 5. The apparatus of claim 1,wherein the magnet comprises an outer magnet diameter less than theinner coil diameter and the inner shield diameter, such that a gap isdefined between the magnet and the substantially annular shield.
 6. Theapparatus of claim 1, wherein the coil comprises an outer coil diameterand the substantially annular shield comprises an outer shield diameter,wherein the outer coil diameter and the outer shield diameter aresubstantially aligned.
 7. The apparatus of claim 1, further comprising asubstrate disposed above the magnet, wherein the substrate at leastpartially defines the volume, and wherein the volume has magnetic fluxpermeability less than the first magnetic flux permeability.
 8. Theapparatus of claim 1, wherein the apparatus further comprises a base andthe coil is disposed between the substantially annular shield and thebase.
 9. An apparatus comprising: an outer volume having a firstmagnetic flux permeability, wherein the outer volume contains: a coilcomprising an inner coil diameter; a shield substantially aligned withand disposed above the coil, wherein the shield comprises an innershield diameter, and wherein the first magnetic flux permeability is atleast partially defined by the shield; and an inner volume having asecond magnetic flux permeability less than the first magnetic fluxpermeability, wherein the inner volume is at least partially defined bythe inner coil diameter and the inner shield diameter, and wherein theinner volume contains a magnet.
 10. The apparatus of claim 9, wherein acenter point of each of the coil, the shield, and the magnet are alignedwith an axis.
 11. The apparatus of claim 9, wherein the coil and theshield are outside of the inner volume.
 12. The apparatus of claim 9,wherein the coil comprises an outer coil diameter and the shieldcomprises an outer shield diameter substantially aligned with the outercoil diameter, and wherein the outer volume is at least partiallydefined by the outer coil diameter and the outer shield diameter. 13.The apparatus of claim 12, wherein the outer volume is substantiallyannular, and wherein the inner volume is substantially cylindrical. 14.The apparatus of claim 13, wherein the inner volume includes a gashaving a magnetic flux permeability that is less than the first magneticflux permeability.
 15. The apparatus of claim 13, wherein the innervolume includes a foam material having a magnetic flux permeability thatis less than the first magnetic flux permeability.
 16. An apparatuscomprising: a coil comprising an inner coil diameter; a shieldcomprising an inner shield diameter, wherein the inner coil diameter andthe inner shield diameter at least partially define a volume, whereinthe shield is configured to redirect a magnetic flux generated by thecoil; and a magnet at least partially disposed within the volume. 17.The apparatus of claim 16, further comprising a substrate disposed abovethe shield, wherein the substrate at least partially defines the volume.18. The apparatus of claim 16, further comprising a base disposed belowthe coil, wherein the base at least partially defines the volume. 19.The apparatus of claim 16, wherein the coil comprises a shape that is atleast one of round, substantially round, oval, substantially oval, andD-shaped.
 20. The apparatus of claim 19, wherein the volume issubstantially cylindrical.